Environmental sensing systems having independent notifications across multiple thresholds

ABSTRACT

A sensor unit that includes at least one sensor configured to measure an ambient condition is described. The controller can be configured to receive instructions, to report a notice level when the controller determines that data measured by the at least one sensor fails a report threshold test corresponding to a report threshold value. The controller can also be configured to obtain a plurality of calibration measurements from the at least one sensor during a calibration period and to adjust the threshold based on the calibration measurements. The controller can be configured to compute a first threshold level corresponding to background noise and a second threshold level corresponding to sensor noise, and to compute the report threshold value from the second threshold. In one embodiment, the sensor unit adjusts one or more of the thresholds based on ambient temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/165,003, filed Jan. 27, 2014, which is a continuation of U.S. patentapplication Ser. No. 12/624,838, filed Nov. 24, 2009, and entitled,“SYSTEM AND METHOD FOR HIGH-SENSITIVITY SENSOR” now U.S. Pat. No.8,638,215, which is a continuation of U.S. patent application Ser. No.11/494,988, filed Jul. 28, 2006, and entitled “SYSTEM AND METHOD FORHIGH-SENSITIVITY SENSOR” now U.S. Pat. No. 7,623,028, which is acontinuation-in-part of U.S. patent application Ser. No. 10/856,390,filed May 27, 2004, and entitled “WIRELESS SENSOR SYSTEM”, now U.S. Pat.No. 7,102,505. The entire disclosures of the above applications arehereby incorporated by reference, for all purposes, as if fully setforth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sensor with improved sensitivity foruse in a wired or wireless sensor system for monitoring potentiallydangerous or costly conditions, such as, for example, smoke,temperature, water, gas and the like.

2. Description of the Related Art

Maintaining and protecting a building or complex is difficult andcostly. Some conditions, such as fires, gas leaks, etc., are a danger tothe occupants and the structure. Other malfunctions, such as water leaksin roofs, plumbing, etc., are not necessarily dangerous for theoccupants, but can, nevertheless, cause considerable damage. In manycases, an adverse condition such as water leakage, fire, etc., is notdetected in the early stages when the damage and/or danger is relativelysmall. Sensors can be used to detect such adverse conditions, butsensors present their own set of problems. For example, adding sensors,such as, for example, smoke detectors, water sensors, and the like in anexisting structure can be prohibitively expensive due to the cost ofinstalling wiring between the remote sensors and a centralizedmonitoring device used to monitor the sensors. Adding wiring to providepower to the sensors further increases the cost. Moreover, with regardto fire sensors, most fire departments will not allow automaticnotification of the fire department based on the data from a smokedetector alone. Most fire departments require that a specifictemperature rate-of-rise be detected before an automatic fire alarmsystem can notify the fire department. Unfortunately, detecting fire bytemperature rate-of-rise generally means that the fire is not detecteduntil it is too late to prevent major damage.

Moreover, most sensors, such as smoke sensors, are configured with afixed threshold. If the sensed quantity (e.g., smoke level) rises abovethe threshold, then an alarm is triggered. Unfortunately, the thresholdlevel must be placed relatively high to avoid false alarms and to allowfor natural aging of components, and to allow for natural variations inthe ambient environment. Setting the threshold to a relatively highlevel avoids false alarms, but reduces the effectiveness of the sensorand can unnecessarily put people and property at risk.

SUMMARY

These and other problems are solved by a sensor unit that includes atleast one sensor configured to measure an ambient condition and acontroller. The controller can be configured to receive instructions, toreport a notice level when the controller determines that data measuredby the at least one sensor fails a report threshold test correspondingto a report threshold value. The controller can also be configured toobtain a plurality of calibration measurements from the at least onesensor during a calibration period and to adjust the threshold based onthe calibration measurements. The controller can be configured tocompute a first threshold level corresponding to background noise and asecond threshold level corresponding to sensor noise, and to compute thereport threshold value from the second threshold. In one embodiment, thesensor unit adjusts one or more of the thresholds based on ambienttemperature.

In one embodiment, the sensor unit includes a fan controlled by thecontroller. The fan is configured to improve air exchange between asensor chamber and ambient air. In one embodiment, the controlleroperates the fan during one or more measurement periods. In oneembodiment, the controller operates the fan prior to one or moremeasurement periods.

In one embodiment, the controller reports a diagnostic error at leastwhen the second threshold does not exceed the first threshold. In oneembodiment, the controller reports a diagnostic error at least when thesecond threshold does not exceed the first threshold. In one embodiment,the controller measures the first threshold and the second threshold inresponse to a command. In one embodiment, the controller measures thefirst threshold and the second threshold at power-up (e.g., when a powersource, such as, for example, batteries, line power etc., are providedto the sensor unit).

In one embodiment, the sensor system provides an adjustable thresholdlevel for the sensed quantity. The adjustable threshold allows thesensor to adjust to ambient conditions, aging of components, and otheroperational variations while still providing a relatively sensitivedetection capability for hazardous conditions. The adjustable thresholdsensor can operate for an extended period of operability withoutmaintenance or recalibration. In one embodiment, the sensor isself-calibrating and runs through a calibration sequence at startup orat periodic intervals. In one embodiment, the adjustable thresholdsensor is used in an intelligent sensor system that includes one or moreintelligent sensor units and a base unit that can communicate with thesensor units. When one or more of the sensor units detects an anomalouscondition (e.g., smoke, fire, water, etc.) the sensor unit communicateswith the base unit and provides data regarding the anomalous condition.The base unit can contact a supervisor or other responsible person by aplurality of techniques, such as, telephone, pager, cellular telephone,Internet (and/or local area network), etc. In one embodiment, one ormore wireless repeaters are used between the sensor units and the baseunit to extend the range of the system and to allow the base unit tocommunicate with a larger number of sensors.

In one embodiment, the adjustable-threshold sensor sets a thresholdlevel according to an average value of the sensor reading. In oneembodiment, the average value is a relatively long-term average. In oneembodiment, the average is a time-weighted average wherein recent sensorreadings used in the averaging process are weighted differently thanless recent sensor readings. The average is used to set the thresholdlevel. When the sensor reading rises above the threshold level, thesensor indicates an alarm condition. In one embodiment, the sensorindicates an alarm condition when the sensor reading rises above thethreshold value for a specified period of time. In one embodiment, thesensor indicates an alarm condition when a statistical number of sensorreadings (e.g., 3 of 2, 5 of 3, 10 of 7, etc.) are above the thresholdlevel. In one embodiment, the sensor indicates various levels of alarm(e.g., notice, alert, alarm) based on how far above the threshold thesensor reading has risen and/or how rapidly the sensor reading hasrisen.

In one embodiment, the sensor system includes a number of sensor unitslocated throughout a building that sense conditions and report anomalousresults back to a central reporting station. The sensor units measureconditions that might indicate a fire, water leak, etc. The sensor unitsreport the measured data to the base unit whenever the sensor unitdetermines that the measured data is sufficiently anomalous to bereported. The base unit can notify a responsible person such as, forexample, a building manager, building owner, private security service,etc. In one embodiment, the sensor units do not send an alarm signal tothe central location. Rather, the sensors send quantitative measureddata (e.g., smoke density, temperature rate of rise, etc.) to thecentral reporting station.

In one embodiment, the sensor system includes a battery-operated sensorunit that detects a condition, such as, for example, smoke, temperature,humidity, moisture, water, water temperature, carbon monoxide, naturalgas, propane gas, other flammable gases, radon, poison gasses, etc. Thesensor unit is placed in a building, apartment, office, residence, etc.In order to conserve battery power, the sensor is normally placed in alow-power mode. In one embodiment, while in the low-power mode, thesensor unit takes regular sensor readings, adjusts the threshold level,and evaluates the readings to determine if an anomalous conditionexists. If an anomalous condition is detected, then the sensor unit“wakes up” and begins communicating with the base unit or with arepeater. At programmed intervals, the sensor also “wakes up” and sendsstatus information to the base unit (or repeater) and then listens forcommands for a period of time.

In one embodiment, the sensor unit is bi-directional and configured toreceive instructions from the central reporting station (or repeater).Thus, for example, the central reporting station can instruct the sensorto: perform additional measurements; go to a standby mode; wake up;report battery status; change wake-up interval; run self-diagnostics andreport results; report its threshold level, change its threshold level,change its threshold calculation equation, change its alarm calculationequation, etc. In one embodiment, the sensor unit also includes a tamperswitch. When tampering with the sensor is detected, the sensor reportssuch tampering to the base unit. In one embodiment, the sensor reportsits general health and status to the central reporting station on aregular basis (e.g., results of self-diagnostics, battery health, etc.).

In one embodiment, the sensor unit provides two wake-up modes, a firstwake-up mode for taking measurements (and reporting such measurements ifdeemed necessary), and a second wake-up mode for listening for commandsfrom the central reporting station. The two wake-up modes, orcombinations thereof, can occur at different intervals.

In one embodiment, the sensor units use spread-spectrum techniques tocommunicate with the base unit and/or the repeater units. In oneembodiment, the sensor units use frequency-hopping spread-spectrum. Inone embodiment, each sensor unit has an Identification code (ID) and thesensor units attaches its ID to outgoing communication packets. In oneembodiment, when receiving wireless data, each sensor unit ignores datathat is addressed to other sensor units.

The repeater unit is configured to relay communications traffic betweena number of sensor units and the base unit. The repeater units typicallyoperate in an environment with several other repeater units and thus,each repeater unit contains a database (e.g., a lookup table) of sensorIDs. During normal operation, the repeater only communicates withdesignated wireless sensor units whose IDs appears in the repeater'sdatabase. In one embodiment, the repeater is battery-operated andconserves power by maintaining an internal schedule of when itsdesignated sensors are expected to transmit and going to a low-powermode when none of its designated sensor units is scheduled to transmit.In one embodiment, the repeater uses spread-spectrum to communicate withthe base unit and the sensor units. In one embodiment, the repeater usesfrequency-hopping spread-spectrum to communicate with the base unit andthe sensor units. In one embodiment, each repeater unit has an ID andthe repeater unit attaches its ID to outgoing communication packets thatoriginate in the repeater unit. In one embodiment, each repeater unitignores data that is addressed to other repeater units or to sensorunits not serviced by the repeater.

In one embodiment, the repeater is configured to provide bi-directionalcommunication between one or more sensors and a base unit. In oneembodiment, the repeater is configured to receive instructions from thecentral reporting station (or repeater). Thus, for example, the centralreporting station can instruct the repeater to: send commands to one ormore sensors; go to standby mode; “wake up”; report battery status;change wake-up interval; run self-diagnostics and report results; etc.

The base unit is configured to receive measured sensor data from anumber of sensor units. In one embodiment, the sensor information isrelayed through the repeater units. The base unit also sends commands tothe repeater units and/or sensor units. In one embodiment, the base unitincludes a diskless PC that runs off of a CD-ROM, flash memory, DVD, orother read-only device, etc. When the base unit receives data from awireless sensor indicating that there may be an emergency condition(e.g., a fire or excess smoke, temperature, water, flammable gas, etc.)the base unit will attempt to notify a responsible party (e.g., abuilding manager) by several communication channels (e.g., telephone,Internet, pager, cell phone, etc.). In one embodiment, the base unitsends instructions to place the wireless sensor in an alert mode(inhibiting the wireless sensor's low-power mode). In one embodiment,the base unit sends instructions to activate one or more additionalsensors near the first sensor.

In one embodiment, the base unit maintains a database of the health,battery status, signal strength, and current operating status of all ofthe sensor units and repeater units in the wireless sensor system. Inone embodiment, the base unit automatically performs routine maintenanceby sending commands to each sensor to run a self-diagnostic and reportthe results. The base unit collects such diagnostic results. In oneembodiment, the base unit sends instructions to each sensor telling thesensor how long to wait between “wakeup” intervals. In one embodiment,the base unit schedules different wakeup intervals to different sensorsbased on the sensor's health, battery health, location, etc. In oneembodiment, the base unit sends instructions to repeaters to routesensor information around a failed repeater.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows sensor system that includes a plurality of sensor unitsthat communicate with a base unit through a number of repeater units

FIG. 2 is a block diagram of a sensor unit.

FIG. 3 is a block diagram of a repeater unit.

FIG. 4 is a block diagram of the base unit.

FIG. 5 shows a network communication packet used by the sensor units,repeater units, and the base unit.

FIG. 6 is a flowchart showing operation of a sensor unit that providesrelatively continuous monitoring.

FIG. 7 is a flowchart showing operation of a sensor unit that providesperiodic monitoring.

FIG. 8 shows how the sensor system can be used to detect water leaks.

FIG. 9 shows an optical smoke sensor configured to operate at arelatively high sensitivity.

FIG. 10 shows a emitter drive pulse and photo-sensor outputs during darktime and during pulse time.

FIG. 11 shows a calibration sequence for the optical smoke sensor ofFIG. 9.

FIG. 12 shows one embodiment of temperature compensation in an opticalsmoke detector.

DETAILED DESCRIPTION

FIG. 1 shows a sensor system 100 that includes a plurality of sensorunits 102-106 that communicate with a base unit 112 through a number ofrepeater units 110-111. The sensor units 102-106 are located throughouta building 101. Sensor units 102-104 communicate with the repeater 110.Sensor units 105-106 communicate with the repeater 111. The repeaters110-111 communicate with the base unit 112. The base unit 112communicates with a monitoring computer system 113 through a computernetwork connection such as, for example, Ethernet, wireless Ethernet,firewire port, Universal Serial Bus (USB) port, bluetooth, etc. Thecomputer system 113 contacts a building manager, maintenance service,alarm service, or other responsible personnel 120 using one or more ofseveral communication systems such as, for example, telephone 121, pager122, cellular telephone 123 (e.g., direct contact, voicemail, text,etc.), and/or through the Internet and/or local area network 124 (e.g.,through email, instant messaging, network communications, etc.). In oneembodiment, multiple base units 112 are provided to the monitoringcomputer 113. In one embodiment, the monitoring computer 113 is providedto more than one computer monitors, thus, allowing more data to bedisplayed than can conveniently be displayed on a single monitor. In oneembodiment, the monitoring computer 113 is provided to multiple monitorslocated in different locations, thus allowing the data from themonitoring computer 113 to be displayed in multiple locations.

The sensor units 102-106 include sensors to measure conditions, such as,for example, smoke, temperature, moisture, water, water temperature,humidity, carbon monoxide, natural gas, propane gas, security alarms,intrusion alarms (e.g., open doors, broken windows, open windows, andthe like), other flammable gases, radon, poison gasses, etc. Differentsensor units can be configured with different sensors or withcombinations of sensors. Thus, for example, in one installation thesensor units 102 and 104 could be configured with smoke and/ortemperature sensors while the sensor unit 103 could be configured with ahumidity sensor.

The discussion that follows generally refers to the sensor unit 102 asan example of a sensor unit, with the understanding that the descriptionof the sensor unit 102 can be applied to many sensor units. Similarly,the discussion generally refers to the repeater 110 by way of example,and not limitation. It will also be understood by one of ordinary skillin the art that repeaters are useful for extending the range of thesensor units 102-106 but are not required in all embodiments. Thus, forexample, in one embodiment, one or more of the sensor units 102-106 cancommunicate directly with the base unit 112 without going through arepeater. It will also be understood by one of ordinary skill in the artthat FIG. 1 shows only five sensor units (102-106) and two repeaterunits (110-111) for purposes of illustration and not by way oflimitation. An installation in a large apartment building or complexwould typically involve many sensor units and repeater units. Moreover,one of ordinary skill in the art will recognize that one repeater unitcan service relatively many sensor units. In one embodiment, the sensorunits 102 can communicate directly with the base unit 112 without goingthrough a repeater 111.

When the sensor unit 102 detects an anomalous condition (e.g., smoke,fire, water, etc.) the sensor unit communicates with the appropriaterepeater unit 110 and provides data regarding the anomalous condition.The repeater unit 110 forwards the data to the base unit 112, and thebase unit 112 forwards the information to the computer 113. The computer113 evaluates the data and takes appropriate action. If the computer 113determines that the condition is an emergency (e.g., fire, smoke, largequantities of water), then the computer 113 contacts the appropriatepersonnel 120. If the computer 113 determines that the situationwarrants reporting, but is not an emergency, then the computer 113 logsthe data for later reporting. In this way, the sensor system 100 canmonitor the conditions in and around the building 101.

In one embodiment, the sensor unit 102 has an internal power source(e.g., battery, solar cell, fuel cell, etc.). In order to conservepower, the sensor unit 102 is normally placed in a low-power mode. Inone embodiment, using sensors that require relatively little power,while in the low-power mode the sensor unit 102 takes regular sensorreadings and evaluates the readings to determine if an anomalouscondition exists. In one embodiment, using sensors that requirerelatively more power, while in the low-power mode, the sensor unit 102takes and evaluates sensor readings at periodic intervals. If ananomalous condition is detected, then the sensor unit 102 “wakes up” andbegins communicating with the base unit 112 through the repeater 110. Atprogrammed intervals, the sensor unit 102 also “wakes up” and sendsstatus information (e.g., power levels, self diagnostic information,etc.) to the base unit (or repeater) and then listens for commands for aperiod of time. In one embodiment, the sensor unit 102 also includes atamper detector. When tampering with the sensor unit 102 is detected,the sensor unit 102 reports such tampering to the base unit 112.

In one embodiment, the sensor unit 102 provides bi-directionalcommunication and is configured to receive data and/or instructions fromthe base unit 112. Thus, for example, the base unit 112 can instruct thesensor unit 102 to perform additional measurements, to go to a standbymode, to wake up, to report battery status, to change wake-up interval,to run self-diagnostics and report results, etc. In one embodiment, thesensor unit 102 reports its general health and status on a regular basis(e.g., results of self-diagnostics, battery health, etc.)

In one embodiment, the sensor unit 102 provides two wake-up modes, afirst wake-up mode for taking measurements (and reporting suchmeasurements if deemed necessary), and a second wake-up mode forlistening for commands from the central reporting station. The twowake-up modes, or combinations thereof, can occur at differentintervals.

In one embodiment, the sensor unit 102 uses spread-spectrum techniquesto communicate with the repeater unit 110. In one embodiment, the sensorunit 102 uses frequency-hopping spread-spectrum. In one embodiment, thesensor unit 102 has an address or identification (ID) code thatdistinguishes the sensor unit 102 from the other sensor units. Thesensor unit 102 attaches its ID to outgoing communication packets sothat transmissions from the sensor unit 102 can be identified by therepeater 110. The repeater 110 attaches the ID of the sensor unit 102 todata and/or instructions that are transmitted to the sensor unit 102. Inone embodiment, the sensor unit 102 ignores data and/or instructionsthat are addressed to other sensor units.

In one embodiment, the sensor unit 102 includes a reset function. In oneembodiment, the reset function is activated by the reset switch 208. Inone embodiment, the reset function is active for a prescribed intervalof time. During the reset interval, the transceiver 203 is in areceiving mode and can receive the identification code from an externalprogrammer. In one embodiment, the external programmer wirelesslytransmits a desired identification code. In one embodiment, theidentification code is programmed by an external programmer that isconnected to the sensor unit 102 through an electrical connector. In oneembodiment, the electrical connection to the sensor unit 102 is providedby sending modulated control signals (power line carrier signals)through a connector used to connect the power source 206. In oneembodiment, the external programmer provides power and control signals.In one embodiment, the external programmer also programs the type ofsensor(s) installed in the sensor unit. In one embodiment, theidentification code includes an area code (e.g., apartment number, zonenumber, floor number, etc.) and a unit number (e.g., unit 1, 2, 3,etc.).

In one embodiment, the sensor communicates with the repeater on the 900MHz band. This band provides good transmission through walls and otherobstacles normally found in and around a building structure. In oneembodiment, the sensor communicates with the repeater on bands aboveand/or below the 900 MHz band. In one embodiment, the sensor, repeater,and/or base unit listens to a radio frequency channel beforetransmitting on that channel or before beginning transmission. If thechannel is in use, (e.g., by another device such as another repeater, acordless telephone, etc.) then the sensor, repeater, and/or base unitchanges to a different channel. In one embodiment, the sensor, repeater,and/or base unit coordinate frequency hopping by listening to radiofrequency channels for interference and using an algorithm to select anext channel for transmission that avoids the interference. Thus, forexample, in one embodiment, if a sensor senses a dangerous condition andgoes into a continuous transmission mode, the sensor will test (e.g.,listen to) the channel before transmission to avoid channels that areblocked, in use, or jammed. In one embodiment, the sensor continues totransmit data until it receives an acknowledgement from the base unitthat the message has been received. In one embodiment, the sensortransmits data having a normal priority (e.g., status information) anddoes not look for an acknowledgement, and the sensor transmits datahaving elevated priority (e.g., excess smoke, temperature, etc.) untilan acknowledgement is received.

The repeater unit 110 is configured to relay communications trafficbetween the sensor 102 (and similarly, the sensor units 103-104) and thebase unit 112. The repeater unit 110 typically operates in anenvironment with several other repeater units (such as the repeater unit111 in FIG. 1) and thus, the repeater unit 110 contains a database(e.g., a lookup table) of sensor unit IDs. In FIG. 1, the repeater 110has database entries for the IDs of the sensors 102-104, and thus, thesensor 110 will only communicate with sensor units 102-104. In oneembodiment, the repeater 110 has an internal power source (e.g.,battery, solar cell, fuel cell, etc.) and conserves power by maintainingan internal schedule of when the sensor units 102-104 are expected totransmit. In one embodiment, the repeater unit 110 goes to a low-powermode when none of its designated sensor units is scheduled to transmit.In one embodiment, the repeater 110 uses spread-spectrum techniques tocommunicate with the base unit 112 and with the sensor units 102-104. Inone embodiment, the repeater 110 uses frequency-hopping spread-spectrumto communicate with the base unit 112 and the sensor units 102-104. Inone embodiment, the repeater unit 110 has an address or identification(ID) code and the repeater unit 110 attaches its address to outgoingcommunication packets that originate in the repeater (that is, packetsthat are not being forwarded). In one embodiment, the repeater unit 110ignores data and/or instructions that are addressed to other repeaterunits or to sensor units not serviced by the repeater 110.

In one embodiment, the base unit 112 communicates with the sensor unit102 by transmitting a communication packet addressed to the sensor unit102. The repeaters 110 and 111 both receive the communication packetaddressed to the sensor unit 102. The repeater unit 111 ignores thecommunication packet addressed to the sensor unit 102. The repeater unit110 transmits the communication packet addressed to the sensor unit 102.In one embodiment, the sensor unit 102, the repeater unit 110, and thebase unit 112 communicate using Frequency-Hopping Spread Spectrum(FHSS), also known as channel-hopping.

Frequency-hopping wireless systems offer the advantage of avoiding otherinterfering signals and avoiding collisions. Moreover, there areregulatory advantages given to systems that do not transmit continuouslyat one frequency. Channel-hopping transmitters change frequencies aftera period of continuous transmission, or when interference isencountered. These systems may have higher transmit power and relaxedlimitations on in-band spurs. FCC regulations limit transmission time onone channel to 400 milliseconds (averaged over 10-20 seconds dependingon channel bandwidth) before the transmitter must change frequency.There is a minimum frequency step when changing channels to resumetransmission. If there are 25 to 49 frequency channels, regulationsallow effective radiated power of 24 dBm, spurs must be −20 dBc, andharmonics must be −41.2 dBc. With 50 or more channels, regulations alloweffective radiated power to be up to 30 dBm.

In one embodiment, the sensor unit 102, the repeater unit 110, and thebase unit 112 communicate using FHSS wherein the frequency hopping ofthe sensor unit 102, the repeater unit 110, and the base unit 112 arenot synchronized such that at any given moment, the sensor unit 102 andthe repeater unit 110 are on different channels. In such a system, thebase unit 112 communicates with the sensor unit 102 using the hopfrequencies synchronized to the repeater unit 110 rather than the sensorunit 102. The repeater unit 110 then forwards the data to the sensorunit using hop frequencies synchronized to the sensor unit 102. Such asystem largely avoids collisions between the transmissions by the baseunit 112 and the repeater unit 110.

In one embodiment, the sensor units 102-106 all use FHSS and the sensorunits 102-106 are not synchronized. Thus, at any given moment, it isunlikely that any two or more of the sensor units 102-106 will transmiton the same frequency. In this manner, collisions are largely avoided.In one embodiment, collisions are not detected but are tolerated by thesystem 100. If a collision does occur, data lost due to the collision iseffectively re-transmitted the next time the sensor units transmitsensor data. When the sensor units 102-106 and repeater units 110-111operate in asynchronous mode, then a second collision is highly unlikelybecause the units causing the collisions have hopped to differentchannels. In one embodiment, the sensor units 102-106, repeater units110-111, and the base unit 112 use the same hop rate. In one embodiment,the sensor units 102-106, repeater units 110-111, and the base unit 112use the same pseudo-random algorithm to control channel hopping, butwith different starting seeds. In one embodiment, the starting seed forthe hop algorithm is calculated from the ID of the sensor units 102-106,repeater units 110-111, or the base unit 112.

In an alternative embodiment, the base unit communicates with the sensorunit 102 by sending a communication packet addressed to the repeaterunit 110, where the packet sent to the repeater unit 110 includes theaddress of the sensor unit 102. The repeater unit 102 extracts theaddress of the sensor unit 102 from the packet and creates and transmitsa packet addressed to the sensor unit 102.

In one embodiment, the repeater unit 110 is configured to providebi-directional communication between its sensors and the base unit 112.In one embodiment, the repeater 110 is configured to receiveinstructions from the base unit 110. Thus, for example, the base unit112 can instruct the repeater to: send commands to one or more sensors;go to standby mode; “wake up”; report battery status; change wake-upinterval; run self-diagnostics and report results; etc.

The base unit 112 is configured to receive measured sensor data from anumber of sensor units either directly, or through the repeaters110-111. The base unit 112 also sends commands to the repeater units110-111 and/or to the sensor units 102-106. In one embodiment, the baseunit 112 communicates with a diskless computer 113 that runs off of aCD-ROM. When the base unit 112 receives data from a sensor unit 102-106indicating that there may be an emergency condition (e.g., a fire orexcess smoke, temperature, water, etc.) the computer 113 will attempt tonotify the responsible party 120.

In one embodiment, the computer 112 maintains a database of the health,power status (e.g., battery charge), and current operating status of allof the sensor units 102-106 and the repeater units 110-111. In oneembodiment, the computer 113 automatically performs routine maintenanceby sending commands to each sensor unit 102-106 to run a self-diagnosticand report the results. The computer 113 collects and logs suchdiagnostic results. In one embodiment, the computer 113 sendsinstructions to each sensor unit 102-106 telling the sensor how long towait between “wakeup” intervals. In one embodiment, the computer 113schedules different wakeup intervals to different sensor unit 102-106based on the sensor unit's health, power status, location, etc. In oneembodiment, the computer 113 schedules different wakeup intervals todifferent sensor unit 102-106 based on the type of data and urgency ofthe data collected by the sensor unit (e.g., sensor units that havesmoke and/or temperature sensors produce data that should be checkedrelatively more often than sensor units that have humidity or moisturesensors). In one embodiment, the base unit sends instructions torepeaters to route sensor information around a failed repeater.

In one embodiment, the computer 113 produces a display that tellsmaintenance personnel which sensor units 102-106 need repair ormaintenance. In one embodiment, the computer 113 maintains a listshowing the status and/or location of each sensor according to the ID ofeach sensor.

In one embodiment, the sensor units 102-106 and/or the repeater units110-111 measure the signal strength of the wireless signals received(e.g., the sensor unit 102 measures the signal strength of the signalsreceived from the repeater unit 110, the repeater unit 110 measures thesignal strength received from the sensor unit 102 and/or the base unit112). The sensor units 102-106 and/or the repeater units 110-111 reportsuch signal strength measurement back to the computer 113. The computer113 evaluates the signal strength measurements to ascertain the healthand robustness of the sensor system 100. In one embodiment, the computer113 uses the signal strength information to re-route wirelesscommunications traffic in the sensor system 100. Thus, for example, ifthe repeater unit 110 goes offline or is having difficulty communicatingwith the sensor unit 102, the computer 113 can send instructions to therepeater unit 111 to add the ID of the sensor unit 102 to the databaseof the repeater unit 111 (and similarly, send instructions to therepeater unit 110 to remove the ID of the sensor unit 102), therebyrouting the traffic for the sensor unit 102 through the router unit 111instead of the router unit 110.

FIG. 2 is a block diagram of the sensor unit 102. In the sensor unit102, one or more sensors 201 and a transceiver 203 are provided to acontroller 202. The controller 202 typically provides power, data, andcontrol information to the sensor(s) 201 and the transceiver 203. Apower source 206 is provided to the controller 202. An optional tampersensor 205 is also provided to the controller 202. A reset device (e.g.,a switch) 208 is proved to the controller 202. In one embodiment, anoptional audio output device 209 is provided. In one embodiment, thesensor 201 is configured as a plug-in module that can be replacedrelatively easily. In one embodiment, a temperature sensor 220 isprovided to the controller 202. In one embodiment, the temperaturesensor 220 is configured to measure ambient temperature.

In one embodiment, the transceiver 203 is based on a TRF 6901transceiver chip from Texas Instruments, Inc. In one embodiment, thecontroller 202 is a conventional programmable microcontroller. In oneembodiment, the controller 202 is based on a Field Programmable GateArray (FPGA), such as, for example, provided by Xilinx Corp. In oneembodiment, the sensor 201 includes an optoelectric smoke sensor with asmoke chamber. In one embodiment, the sensor 201 includes a thermistor.In one embodiment, the sensor 201 includes a humidity sensor. In oneembodiment, the sensor 201 includes a sensor, such as, for example, awater level sensor, a water temperature sensor, a carbon monoxidesensor, a moisture sensor, a water flow sensor, natural gas sensor,propane sensor, etc.

The controller 202 receives sensor data from the sensor(s) 201. Somesensors 201 produce digital data. However, for many types of sensors201, the sensor data is analog data. Analog sensor data is converted todigital format by the controller 202. In one embodiment, the controllerevaluates the data received from the sensor(s) 201 and determineswhether the data is to be transmitted to the base unit 112. The sensorunit 102 generally conserves power by not transmitting data that fallswithin a normal range. In one embodiment, the controller 202 evaluatesthe sensor data by comparing the data value to a threshold value (e.g.,a high threshold, a low threshold, or a high-low threshold). If the datais outside the threshold (e.g., above a high threshold, below a lowthreshold, outside an inner range threshold, or inside an outer rangethreshold), then the data is deemed to be anomalous and is transmittedto the base unit 112. In one embodiment, the data threshold isprogrammed into the controller 202. In one embodiment, the datathreshold is programmed by the base unit 112 by sending instructions tothe controller 202. In one embodiment, the controller 202 obtains sensordata and transmits the data when commanded by the computer 113.

In one embodiment, the tamper sensor 205 is configured as a switch thatdetects removal of/or tampering with the sensor unit 102.

FIG. 3 is a block diagram of the repeater unit 110. In the repeater unit110, a first transceiver 302 and a second transceiver 304 are providedto a controller 303. The controller 303 typically provides power, data,and control information to the transceivers 302, 304. A power source 306is provided to the controller 303. An optional tamper sensor (not shown)is also provided to the controller 303.

When relaying sensor data to the base unit 112, the controller 303receives data from the first transceiver 302 and provides the data tothe second transceiver 304. When relaying instructions from the baseunit 112 to a sensor unit, the controller 303 receives data from thesecond transceiver 304 and provides the data to the first transceiver302. In one embodiment, the controller 303 conserves power bypowering-down the transceivers 302, 304 during periods when thecontroller 303 is not expecting data. The controller 303 also monitorsthe power source 306 and provides status information, such as, forexample, self-diagnostic information and/or information about the healthof the power source 306, to the base unit 112. In one embodiment, thecontroller 303 sends status information to the base unit 112 at regularintervals. In one embodiment, the controller 303 sends statusinformation to the base unit 112 when requested by the base unit 112. Inone embodiment, the controller 303 sends status information to the baseunit 112 when a fault condition (e.g., battery low) is detected.

In one embodiment, the controller 303 includes a table or list ofidentification codes for wireless sensor units 102. The repeater 110forwards packets received from, or sent to, sensor units 102 in thelist. In one embodiment, the repeater 110 receives entries for the listof sensor units from the computer 113. In one embodiment, the controller303 determines when a transmission is expected from the sensor units 102in the table of sensor units and places the repeater 110 (e.g., thetransceivers 302, 304) in a low-power mode when no transmissions areexpected from the transceivers on the list. In one embodiment, thecontroller 303 recalculates the times for low-power operation when acommand to change reporting interval is forwarded to one of the sensorunits 102 in the list (table) of sensor units or when a new sensor unitis added to the list (table) of sensor units.

FIG. 4 is a block diagram of the base unit 112. In the base unit 112, atransceiver 402 and a computer interface 404 are provided to acontroller 403. The controller 403 typically provides data and controlinformation to the transceivers 402 and to the interface. The interface404 is provided to a port on the monitoring computer 113. The interface404 can be a standard computer data interface, such as, for example,Ethernet, wireless Ethernet, firewire port, Universal Serial Bus (USB)port, bluetooth, etc.

FIG. 5 shows a communication packet 500 used by the sensor units,repeater units, and the base unit. The packet 500 includes a preambleportion 501, an address (or ID) portion 502, a data payload portion 503,and an integrity portion 504. In one embodiment, the integrity portion504 includes a checksum. In one embodiment, the sensor units 102-106,the repeater units 110-111, and the base unit 112 communicate usingpackets such as the packet 500. In one embodiment, the packets 500 aretransmitted using FHSS.

In one embodiment, the data packets that travel between the sensor unit102, the repeater unit 111, and the base unit 112 are encrypted. In oneembodiment, the data packets that travel between the sensor unit 102,the repeater unit 111, and the base unit 112 are encrypted and anauthentication code is provided in the data packet so that the sensorunit 102, the repeater unit, and/or the base unit 112 can verify theauthenticity of the packet.

In one embodiment the address portion 502 includes a first code and asecond code. In one embodiment, the repeater 111 only examines the firstcode to determine if the packet should be forwarded. Thus, for example,the first code can be interpreted as a building (or building complex)code and the second code interpreted as a subcode (e.g., an apartmentcode, area code, etc.). A repeater that uses the first code forforwarding, thus, forwards packets having a specified first code (e.g.,corresponding to the repeater's building or building complex). Thus,alleviates the need to program a list of sensor units 102 into arepeater, since a group of sensors in a building will typically all havethe same first code but different second codes. A repeater soconfigured, only needs to know the first code to forward packets for anyrepeater in the building or building complex. This does, however, raisethe possibility that two repeaters in the same building could try toforward packets for the same sensor unit 102. In one embodiment, eachrepeater waits for a programmed delay period before forwarding a packet.Thus, reducing the chance of packet collisions at the base unit (in thecase of sensor unit to base unit packets) and reducing the chance ofpacket collisions at the sensor unit (in the case of base unit to sensorunit packets). In one embodiment, a delay period is programmed into eachrepeater. In one embodiment, delay periods are pre-programmed onto therepeater units at the factory or during installation. In one embodiment,a delay period is programmed into each repeater by the base unit 112. Inone embodiment, a repeater randomly chooses a delay period. In oneembodiment, a repeater randomly chooses a delay period for eachforwarded packet. In one embodiment, the first code is at least 6digits. In one embodiment, the second code is at least 5 digits.

In one embodiment, the first code and the second code are programmedinto each sensor unit at the factory. In one embodiment, the first codeand the second code are programmed when the sensor unit is installed. Inone embodiment, the base unit 112 can re-program the first code and/orthe second code in a sensor unit.

In one embodiment, collisions are further avoided by configuring eachrepeater unit 111 to begin transmission on a different frequencychannel. Thus, if two repeaters attempt to begin transmission at thesame time, the repeaters will not interfere with each other because thetransmissions will begin on different channels (frequencies).

FIG. 6 is a flowchart showing one embodiment of the operation of thesensor unit 102 wherein relatively continuous monitoring is provided. InFIG. 6, a power up block 601 is followed by an initialization block 602.After initialization, the sensor unit 102 checks for a fault condition(e.g., activation of the tamper sensor, low battery, internal fault,etc.) in a block 603. A decision block 604 checks the fault status. If afault has occurred, then the process advances to a block 605 were thefault information is transmitted to the repeater 110 (after which, theprocess advances to a block 612); otherwise, the process advances to ablock 606. In the block 606, the sensor unit 102 takes a sensor readingfrom the sensor(s) 201. The sensor data is subsequently evaluated in ablock 607. If the sensor data is abnormal, then the process advances toa transmit block 609 where the sensor data is transmitted to therepeater 110 (after which, the process advances to a block 612);otherwise, the process advances to a timeout decision block 610. If thetimeout period has not elapsed, then the process returns to thefault-check block 603; otherwise, the process advances to a transmitstatus block 611 where normal status information is transmitted to therepeater 110. In one embodiment, the normal status informationtransmitted is analogous to a simple “ping” which indicates that thesensor unit 102 is functioning normally. After the block 611, theprocess proceeds to a block 612 where the sensor unit 102 momentarilylistens for instructions from the monitor computer 113. If aninstruction is received, then the sensor unit 102 performs theinstructions, otherwise, the process returns to the status check block603. In one embodiment, transceiver 203 is normally powered down. Thecontroller 202 powers up the transceiver 203 during execution of theblocks 605, 609, 611, and 612. The monitoring computer 113 can sendinstructions to the sensor unit 102 to change the parameters used toevaluate data used in block 607, the listen period used in block 612,etc.

Relatively continuous monitoring, such as shown in FIG. 6, isappropriate for sensor units that sense relatively high-priority data(e.g., smoke, fire, carbon monoxide, flammable gas, etc.). By contrast,periodic monitoring can be used for sensors that sense relatively lowerpriority data (e.g., humidity, moisture, water usage, etc.). FIG. 7 is aflowchart showing one embodiment of operation of the sensor unit 102wherein periodic monitoring is provided. In FIG. 7, a power up block 701is followed by an initialization block 702. After initialization, thesensor unit 102 enters a low-power sleep mode 703. If a fault occursduring the sleep mode 703 (e.g., the tamper sensor is activated), thenthe process enters a wake-up block 704 followed by a transmit faultblock 705. If no fault occurs during the sleep period, then when thespecified sleep period has expired, the process enters a block 706 wherethe sensor unit 102 takes a sensor reading from the sensor(s) 201. Thesensor data is subsequently sent to the monitoring computer 113 in areport block 707. After reporting, the sensor unit 102 enters a listenblock 708 where the sensor unit 102 listens for a relatively shortperiod of time for instructions from monitoring computer. If aninstruction is received, then the sensor unit 102 performs theinstructions, otherwise, the process returns to the sleep block 703. Inone embodiment, the sensor 201 and transceiver 203 are normally powereddown. The controller 202 powers up the sensor 201 during execution ofthe block 706. The controller 202 powers up the transceiver duringexecution of the blocks 705, 707, and 708. The monitoring computer 113can send instructions to the sensor unit 102 to change the sleep periodused in block 703, the listen period used in block 708, etc.

In one embodiment, the sensor unit transmits sensor data until ahandshaking-type acknowledgement is received. Thus, rather than sleep ifno instructions or acknowledgements are received after transmission(e.g., after the decision block 613 or 709) the sensor unit 102retransmits its data and waits for an acknowledgement. The sensor unit102 continues to transmit data and wait for an acknowledgement until anacknowledgement is received. In one embodiment, the sensor unit acceptsan acknowledgement from a repeater unit 111 and it then becomes theresponsibility of the repeater unit 111 to make sure that the data isforwarded to the base unit 112. In one embodiment, the repeater unit 111does not generate the acknowledgement, but rather forwards anacknowledgement from the base unit 112 to the sensor unit 102. Thetwo-way communication ability of the sensor unit 102 provides thecapability for the base unit 112 to control the operation of the sensorunit 102 and also provides the capability for robust handshaking-typecommunication between the sensor unit 102 and the base unit 112.

Regardless of the normal operating mode of the sensor unit 102 (e.g.,using the Flowcharts of FIGS. 6, 7, or other modes) in one embodiment,the monitoring computer 113 can instruct the sensor unit 102 to operatein a relatively continuous mode where the sensor repeatedly takes sensorreadings and transmits the readings to the monitoring computer 113. Sucha mode would can be used, for example, when the sensor unit 102 (or anearby sensor unit) has detected a potentially dangerous condition(e.g., smoke, rapid temperature rise, etc.)

FIG. 8 shows the sensor system used to detect water leaks. In oneembodiment, the sensor unit 102 includes a water level sensor 803 and/ora water temperature sensor 804. The water level sensor 803 and/or watertemperature sensor 804 are placed, for example, in a tray underneath awater heater 801 in order to detect leaks from the water heater 801 andthereby, prevent water damage from a leaking water heater. In oneembodiment, an temperature sensor is also provided to measuretemperature near the water heater. The water level sensor can also beplaced under a sink, in a floor sump, etc. In one embodiment, theseverity of a leak is ascertained by the sensor unit 102 (or themonitoring computer 113) by measuring the rate of rise in the waterlevel. When placed near the hot water tank 801, the severity of a leakcan also be ascertained at least in part by measuring the temperature ofthe water. In one embodiment, a first water flow sensor is placed in aninput water line for the hot water tank 801 and a second water flowsensor is placed in an output water line for the hot water tank. Leaksin the tank can be detected by observing a difference between the waterflowing through the two sensors.

In one embodiment, a remote shutoff valve 810 is provided, so that themonitoring system 100 can shutoff the water supply to the water heaterwhen a leak is detected. In one embodiment, the shutoff valve iscontrolled by the sensor unit 102. In one embodiment, the sensor unit102 receives instructions from the base unit 112 to shut off the watersupply to the heater 801. In one embodiment, the responsible party 120sends instructions to the monitoring computer 113 instructing themonitoring computer 113 to send water shut off instructions to thesensor unit 102. Similarly, in one embodiment, the sensor unit 102controls a gas shutoff valve 811 to shut off the gas supply to the waterheater 801 and/or to a furnace (not shown) when dangerous conditions(such as, for example, gas leaks, carbon monoxide, etc.) are detected.In one embodiment, a gas detector 812 is provided to the sensor unit102. In one embodiment, the gas detector 812 measures carbon monoxide.In one embodiment, the gas detector 812 measures flammable gas, such as,for example, natural gas or propane.

In one embodiment, an optional temperature sensor 818 is provided tomeasure stack temperature. Using data from the temperature sensor 818,the sensor unit 102 reports conditions, such as, for example, excessstack temperature. Excess stack temperature is often indicative of poorheat transfer (and thus poor efficiency) in the water heater 818.

In one embodiment, an optional temperature sensor 819 is provided tomeasure temperature of water in the water heater 810. Using data fromthe temperature sensor 819, the sensor unit 102 reports conditions, suchas, for example, over-temperature or under-temperature of the water inthe water heater.

In one embodiment, an optional current probe 821 is provided to measureelectric current provided to a heating element 820 in an electric waterheater. Using data from the current probe 821, the sensor unit 102reports conditions, such as, for example, no current (indicating aburned-out heating element 820). An over-current condition oftenindicates that the heating element 820 is encrusted with mineraldeposits and needs to be replaced or cleaned. By measuring the currentprovided to the water heater, the monitoring system can measure theamount of energy provided to the water heater and thus the cost of hotwater, and the efficiency of the water heater.

In one embodiment, the sensor 803 includes a moisture sensor. Using datafrom the moisture sensor, the sensor unit 102 reports moistureconditions, such as, for example, excess moisture that would indicate awater leak, excess condensation, etc.

In one embodiment, the sensor unit 102 is provided to a moisture sensor(such as the sensor 803) located near an air conditioning unit. Usingdata from the moisture sensor, the sensor unit 102 reports moistureconditions, such as, for example, excess moisture that would indicate awater leak, excess condensation, etc.

In one embodiment, the sensor 201 includes a moisture sensor. Themoisture sensor can be placed under a sink or a toilet (to detectplumbing leaks) or in an attic space (to detect roof leaks).

Excess humidity in a structure can cause severe problems such asrotting, growth of molds, mildew, and fungus, etc. (hereinafter referredto generically as fungus). In one embodiment, the sensor 201 includes ahumidity sensor. The humidity sensor can be placed under a sink, in anattic space, etc., to detect excess humidity (due to leaks,condensation, etc.). In one embodiment, the monitoring computer 113compares humidity measurements taken from different sensor units inorder to detect areas that have excess humidity. Thus, for example, themonitoring computer 113 can compare the humidity readings from a firstsensor unit 102 in a first attic area, to a humidity reading from asecond sensor unit 102 in a second area. For example, the monitoringcomputer can take humidity readings from a number of attic areas toestablish a baseline humidity reading and then compare the specifichumidity readings from various sensor units to determine if one or moreof the units are measuring excess humidity. The monitoring computer 113would flag areas of excess humidity for further investigation bymaintenance personnel. In one embodiment, the monitoring computer 113maintains a history of humidity readings for various sensor units andflags areas that show an unexpected increase in humidity forinvestigation by maintenance personnel.

In one embodiment, the monitoring system 100 detects conditionsfavorable for fungus (e.g., mold, mildew, fungus, etc.) growth by usinga first humidity sensor located in a first building area to producefirst humidity data and a second humidity sensor located in a secondbuilding area to produce second humidity data. The building areas canbe, for example, areas near a sink drain, plumbing fixture, plumbing,attic areas, outer walls, a bilge area in a boat, etc.

The monitoring station 113 collects humidity readings from the firsthumidity sensor and the second humidity sensor and indicates conditionsfavorable for fungus growth by comparing the first humidity data and thesecond humidity data. In one embodiment, the monitoring station 113establishes a baseline humidity by comparing humidity readings from aplurality of humidity sensors and indicates possible fungus growthconditions in the first building area when at least a portion of thefirst humidity data exceeds the baseline humidity by a specified amount.In one embodiment, the monitoring station 113 establishes a baselinehumidity by comparing humidity readings from a plurality of humiditysensors and indicates possible fungus growth conditions in the firstbuilding area when at least a portion of the first humidity data exceedsthe baseline humidity by a specified percentage.

In one embodiment, the monitoring station 113 establishes a baselinehumidity history by comparing humidity readings from a plurality ofhumidity sensors and indicates possible fungus growth conditions in thefirst building area when at least a portion of the first humidity dataexceeds the baseline humidity history by a specified amount over aspecified period of time. In one embodiment, the monitoring station 113establishes a baseline humidity history by comparing humidity readingsfrom a plurality of humidity sensors over a period of time and indicatespossible fungus growth conditions in the first building area when atleast a portion of the first humidity data exceeds the baseline humidityby a specified percentage of a specified period of time.

In one embodiment, the sensor unit 102 transmits humidity data when itdetermines that the humidity data fails a threshold test. In oneembodiment, the humidity threshold for the threshold test is provided tothe sensor unit 102 by the monitoring station 113. In one embodiment,the humidity threshold for the threshold test is computed by themonitoring station from a baseline humidity established in themonitoring station. In one embodiment, the baseline humidity is computedat least in part as an average of humidity readings from a number ofhumidity sensors. In one embodiment, the baseline humidity is computedat least in part as a time average of humidity readings from a number ofhumidity sensors. In one embodiment, the baseline humidity is computedat least in part as a time average of humidity readings from a humiditysensor. In one embodiment, the baseline humidity is computed at least inpart as the lesser of a maximum humidity reading an average of a numberof humidity readings.

In one embodiment, the sensor unit 102 reports humidity readings inresponse to a query by the monitoring station 113. In one embodiment,the sensor unit 102 reports humidity readings at regular intervals. Inone embodiment, a humidity interval is provided to the sensor unit 102by the monitoring station 113.

In one embodiment, the calculation of conditions for fungus growth iscomparing humidity readings from one or more humidity sensors to thebaseline (or reference) humidity. In one embodiment, the comparison isbased on comparing the humidity readings to a percentage (e.g.,typically a percentage greater than 100%) of the baseline value. In oneembodiment, the comparison is based on comparing the humidity readingsto a specified delta value above the reference humidity. In oneembodiment, the calculation of likelihood of conditions for fungusgrowth is based on a time history of humidity readings, such that thelonger the favorable conditions exist, the greater the likelihood offungus growth. In one embodiment, relatively high humidity readings overa period of time indicate a higher likelihood of fungus growth thanrelatively high humidity readings for short periods of time. In oneembodiment, a relatively sudden increase in humidity as compared to abaseline or reference humidity is reported by the monitoring station 113as a possibility of a water leak. If the relatively high humidityreading continues over time then the relatively high humidity isreported by the monitoring station 113 as possibly being a water leakand/or an area likely to have fungus growth or water damage.

Temperatures relatively more favorable to fungus growth increase thelikelihood of fungus growth. In one embodiment, temperature measurementsfrom the building areas are also used in the fungus grown-likelihoodcalculations. In one embodiment, a threshold value for likelihood offungus growth is computed at least in part as a function of temperature,such that temperatures relatively more favorable to fungus growth resultin a relatively lower threshold than temperatures relatively lessfavorable for fungus growth. In one embodiment, the calculation of alikelihood of fungus growth depends at least in part on temperature suchthat temperatures relatively more favorable to fungus growth indicate arelatively higher likelihood of fungus growth than temperaturesrelatively less favorable for fungus growth. Thus, in one embodiment, amaximum humidity and/or minimum threshold above a reference humidity isrelatively lower for temperature more favorable to fungus growth thanthe maximum humidity and/or minimum threshold above a reference humidityfor temperatures relatively less favorable to fungus growth.

In one embodiment, a water flow sensor is provided to the sensor unit102. The sensor unit 102 obtains water flow data from the water flowsensor and provides the water flow data to the monitoring computer 113.The monitoring computer 113 can then calculate water usage.Additionally, the monitoring computer can watch for water leaks, by, forexample, looking for water flow when there should be little or no flow.Thus, for example, if the monitoring computer detects water usagethroughout the night, the monitoring computer can raise an alertindicating that a possible water leak has occurred.

In one embodiment, the sensor 201 includes a water flow sensor providedto the sensor unit 102. The sensor unit 102 obtains water flow data fromthe water flow sensor and provides the water flow data to the monitoringcomputer 113. The monitoring computer 113 can then calculate waterusage. Additionally, the monitoring computer can watch for water leaks,by, for example, looking for water flow when there should be little orno flow. Thus, for example, if the monitoring computer detects waterusage throughout the night, the monitoring computer can raise an alertindicating that a possible water leak has occurred.

In one embodiment, the sensor 201 includes a fire-extinguisher tampersensor provided to the sensor unit 102. The fire-extinguisher tampersensor reports tampering with or use of a fire-extinguisher. In oneembodiment the fire-extinguisher tamper sensor reports that the fireextinguisher has been removed from its mounting, that a fireextinguisher compartment has been opened, and/or that a safety lock onthe fire extinguisher has been removed.

In one embodiment, the sensor unit 102 is configured as anadjustable-threshold sensor that computes a reporting threshold level.In one embodiment, the reporting threshold is computed as an average ofa number of sensor measurements. In one embodiment, the average value isa relatively long-term average. In one embodiment, the average is atime-weighted average wherein recent sensor readings used in theaveraging process are weighted differently than less recent sensorreadings. In one embodiment, more recent sensor readings are weightedrelatively more heavily than less recent sensor readings. In oneembodiment, more recent sensor readings are weighted relatively lessheavily than less recent sensor readings. The average is used to set thereporting threshold level. When the sensor readings rise above thereporting threshold level, the sensor indicates a notice condition. Inone embodiment, the sensor indicates a notice condition when the sensorreading rises above the reporting threshold value for a specified periodof time. In one embodiment, the sensor indicates a notice condition whena statistical number of sensor readings (e.g., 3 of 2, 5 of 3, 10 of 7,etc.) are above the reporting threshold level. In one embodiment, thesensor unit 102 indicates various levels of alarm (e.g., warning, alert,alarm) based on how far above the reporting threshold the sensor readinghas risen.

In one embodiment, the sensor unit 102 computes the notice levelaccording to how far the sensor readings have risen above the thresholdand how rapidly the sensor readings have risen. For example, forpurposes of explanation, the level of readings and the rate of rise canbe quantified as low, medium, and high. The combination of sensorreading level and rate of rise then can be shown as a table, as shown inTable 1. Table 1 provides examples and is provided by way ofexplanation, not limitation.

TABLE 1 Sensor Reading Level (as compared to the reporting thresholdRate of High Warning Alarm Alarm Rise Medium Notice Warning Alarm LowNotice Warning Alarm Low Medium High

One of ordinary skill in the art will recognize that the notice level Ncan be expressed as an equation N=f(t, v, r), where t is the reportingthreshold level, v is the sensor reading, and r is the rate of rise ofthe sensor reading. In one embodiment, the sensor reading v and/or therate of rise r are lowpass filtered in order to reduce the effects ofnoise in the sensor readings. In one embodiment, the reporting thresholdis computed by lowpass filtering the sensor readings v using a filterwith a relatively low cutoff frequency. A filter with a relatively lowcutoff frequency produces a relatively long-term averaging effect. Inone embodiment, separate reporting thresholds are computed for thesensor reading and for the rate of rise.

In one embodiment, a calibration procedure period is provided when thesensor unit 102 is powered up. During the calibration period, the sensordata values from the sensor 201 are used to compute one or morethresholds, but the sensor does not compute notices, warnings, alarms,etc., until the calibration period is complete. In one embodiment, thesensor unit 102 uses a fixed (e.g., pre-programmed) threshold value tocompute notices, warnings, and alarms during the calibration period andthen uses the adjustable reporting threshold value once the calibrationperiod has ended.

In one embodiment, the sensor unit 102 determines that a failure of thesensor 201 has occurred when the adjustable reporting threshold valueexceeds a maximum adjustable threshold value. In one embodiment, thesensor unit 102 determines that a failure of the sensor 201 has occurredwhen the adjustable threshold value falls below a minimum adjustablethreshold value. The sensor unit 102 can report such failure of thesensor 201 to the base unit 112.

In one embodiment, the sensor unit 102 obtains a number of sensor datareadings from the sensor 201 and computes one or more calibration and/orreporting thresholds as a weighted average using a weight vector. Theweight vector weighs some sensor data readings relatively more thanother sensor data readings.

In one embodiment, the sensor unit 102 obtains a number of sensor datareadings from the sensor unit 201 and filters the sensor data readingsand calculates the threshold value from the filtered sensor datareadings. In one embodiment, the sensor unit applies a lowpass filter.In one embodiment, the sensor unit 201 uses a Kalman filter to removeunwanted components from the sensor data readings. In one embodiment,the sensor unit 201 discards sensor data readings that are “outliers”(e.g., too far above or too far below a normative value). In thismanner, the sensor unit 102 can compute the threshold value even in thepresence of noisy sensor data.

In one embodiment, the sensor unit 102 indicates a notice condition(e.g., alert, warning, alarm) when the reporting threshold value changestoo rapidly. In one embodiment, the sensor unit 102 indicates a noticecondition (e.g., alert, warning, alarm) when the threshold value exceedsa specified maximum value. In one embodiment, the sensor unit 102indicates a notice condition (e.g., alert, warning, alarm) when thethreshold value falls below a specified minimum value.

In one embodiment, the sensor unit 102 adjusts one or more operatingparameters of the sensor 201 according to one or more threshold values.Thus, for example, in the example of an optical smoke sensor, the sensorunit 201 can reduce the power used to drive the LED in the optical smokesensor when the threshold value indicates that the optical smoke sensorcan be operated at lower power (e.g., low ambient light conditions,clean sensor, low air particulate conditions, etc.). The sensor unit 201can increase the power used to drive the LED when the threshold valueindicates that the optical smoke sensor should be operated at higherpower (e.g., high ambient light, dirty sensor, higher particulates inthe air, etc.).

In one embodiment, an output from a Heat Ventilating and/or AirConditioning (HVAC) system 350 is optionally provided to the sensor unit102 as shown in FIG. 2. In one embodiment, an output from the HVACsystem 350 is optionally provided to the repeater 110 as shown in FIG. 3and/or to the monitoring system 113 as shown in FIG. 4. In this manner,the system 100 is made aware of the operation of the HVAC system. Whenthe HVAC system turns on or off, the airflow patterns in the roomchange, and thus, the way in which smoke or other materials (e.g.,flammable gases, toxic gases, etc.) changes as well. Thus, in oneembodiment, the threshold calculation takes into account the airfloweffects caused by the HVAC system. In one embodiment, an adaptivealgorithm is used to allow the sensor unit 102 (or monitoring system113) to “learn” how the HVAC system affects sensor readings and thus,the sensor unit 102 (or monitoring system 113) can adjust the thresholdlevel accordingly. In one embodiment, the threshold level is temporarilychanged for a period of time (e.g., raised or lowered) to avoid falsealarms when the HVAC system turns on or off Once the airflow patterns inthe room have re-adjusted to the HVAC state, then the threshold levelcan be re-established for desired system sensitivity.

Thus, for example, in one embodiment where an averaging or lowpassfilter type process is used to establish the threshold level, thethreshold level is temporarily set to de-sensitize the sensor unit 102when the HVAC system turns on or off, thus allowing the averaging orlowpass filtering process to establish a new threshold level. Once a newthreshold level is established (or after a specified period of time),then the sensor unit 102 returns to its normal sensitivity based on thenew threshold level.

In one embodiment, the sensor 201 is configured as an infrared sensor.In one embodiment, the sensor 201 is configured as an infrared sensor tomeasure a temperature of objects within a field of view of the sensor201. In one embodiment, the sensor 201 is configured as an infraredsensor. In one embodiment, the sensor 201 is configured as an infraredsensor to detect flames within a field of view of the sensor 201. In oneembodiment, the sensor 201 is configured as an infrared sensor.

In one embodiment, the sensor 201 is configured as an imaging sensor. Inone embodiment, the controller 202 is configured to detect flames byprocessing of image data from the imaging sensor.

FIG. 9 shows an optical smoke sensor 900 configured to operate at arelatively high sensitivity. The smoke sensor 900 is one embodiment ofthe sensor 201. The smoke sensor 900 includes a chamber 901, an emitter902 provided to the chamber 901, and a photo-sensor 903 provided to thechamber 901. The emitter 902 and photo-sensor 903 are configured tosense smoke in a region 950 of the smoke chamber 901. In one embodiment,an optional temperature sensor 920 is also provided to the chamber 901.A driver 905 is provided to the emitter 902. The photo-sensor 903 isprovided to an amplifier 906. In one embodiment, the emitter 902 emitsinfrared light and the photo-sensor 903 senses infrared light. In oneembodiment, the emitter 902 emits visible light and the photo-sensor 903senses visible light. In one embodiment, the emitter 902 is configuredas a plurality of emitters and/or a multi-spectrum emitter configured toemit light in a plurality of wavelengths (e g, infrared light, redlight, green light, blue light, ultraviolet light, etc.) and thephoto-sensor 903 is configured as a plurality of photo-sensors and/ormulti-spectral sensors to sense the plurality of wavelengths emitted bythe emitter 902. In one embodiment, the photo-sensor 903 is configuredto sense light in a band or bands corresponding to light emitted by theemitter 902 and to reject light in other bands. In one embodiment, thephoto-sensor 903 is configured to sense light in a selected wavelengthband corresponding to light emitted by the emitter 902 and to rejectlight in other bands. In one embodiment one or more filters are providedto the photo-sensor 903 to make the photo-sensor 903 relativelyinsensitive to light in undesired wavelengths.

The optional temperature sensor 920 is provided to an interface 921. Inone embodiment, an optional fan 930 is provided to the smoke chamber901. The fan 930 can be provided within the smoke chamber 901 and/or thefan 930 can be provided external to the smoke chamber 901. The fan 930is configured to increase airflow and air exchange between the smokechamber 901 and the region outside the smoke chamber 901. The fan 930can be conventional rotary fan, a piezoelectric fan, etc.

In one embodiment, an optional calibration module 941 is provided by thesensor 900 to the controller 202. As described in more detail below, thecalibration module 941 can provide calibration data for the sensor unit900 and/or software for the sensor unit 900.

In operation, the driver 905 generates one or more drive pulses inresponse to commands from the controller 202. The drive pulses areprovided to the emitter 902 which generates optical radiation in thechamber 901. The photo-sensor 903 senses the optical radiation from theemitter 902 (e.g., as radiation scattered by the chamber, radiationscattered by smoke in the chamber, etc.). The amplifier 906 amplifiessignals from the photo-sensor 903 and provides the sensor data to thecontroller 202. In one embodiment, the amplifier 906 includes one ormore temperature sensors 916 that provides temperature compensation tocorrect temperature variations of the photo-sensor 903. The temperaturecompensation of the amplifier 906 at least partially stabilizes thesignals from the photo-sensor 903 and thus, allows the sensor 900 to beoperated at relatively higher sensitivity while reducing the number oftemperature-created false alarms.

FIG. 10 shows an emitter drive pulse 1001 and photo-sensor output 1002during dark time 1003 and during pulse time 1004 (when the emitter drivepulse is driving the emitter 902). The sensor unit 900 can be calibratedat least in part by collecting data from the photo-sensor 903 during thedark time 1003 and during the pulse time 1004. During the dark time1003, the emitter 902 is producing little or no radiation, and thus, thesignals produced by the photo-sensor 903 are not due to radiationemitted by the emitter 902, but rather are produced by ambient lightand/or by the photo-sensor 902 itself (e.g., thermal noise, radiointerference, etc.). Thus, the signals produced by the photo-sensor 903during the dark time 1003 can be used to establish a first backgroundlevel or first reference level for the sensor 900. A second referencelevel can be established by measuring the output of the photo-sensor 903during the pulse time 1004 when smoke is not present (or not expected tobe present). In a scattering sensor, the photo-sensor 903 does notdirectly receive radiation from the emitter 902, but rather receivesradiation from the emitter 902 that is scattered by smoke, water vapor,the chamber 901, etc. When no smoke, water vapor, and the like ispresent, then the difference between the first reference level and thesecond reference level is due to scattering from the chamber 901. If thesecond reference level is relatively higher than the first referencelevel, then the controller 202 knows that the emitter 902 andphoto-sensor 903 are operating and that the emitter is producing enoughradiation to overcome the ambient light and other background noise. Ifthe second reference level does not rise above the first referencelevel, the controller can, in one embodiment, instruct the driver 905 toincrease the drive pulse and thus, produce more radiation from theemitter 902. If the second reference level is not higher than the firstreference level (e.g., during operation or, if provided, afterincreasing the drive pulse), then the controller 202 can send a faultmessage to the base unit 113 indicating that a fault has occurred in thesensor 900. If no fault is detected, then the smoke measurements areobtained by comparing sensor measure data with second reference level.Smoke is detected when the measured data from the sensor exceeds thesecond reference level by a specified amount.

FIG. 11 shows a calibration sequence 1100 for the optical smoke sensorof FIG. 9. At power-up 1101, it is assumed that there is no smokepresent and the controller 202 takes one or more calibrationmeasurements using the sensor 900. A first set of calibrationmeasurements is taken during the dark period 1003. A second set ofcalibration measurements is taken during the pulse period 1004. In oneembodiment, the largest measurement during the pulse period 1004 is usedas the second reference level. In one embodiment, an average of severalof the relatively largest measurements during the pulse period 1004 isused as the second reference level.

The optional fan 930 can advantageously be used to increase air/smokeexchange between the chamber 901 and the air/smoke in the room. In oneembodiment, the fan 930 is controlled by the controller 202 such thatthe controller 202 determines when, and if, the fan 930 is operated.Since operation of the fan 930 may reduce battery life, in oneembodiment, the controller 202 operates the fan 930 on an intermittentbasis in connection with smoke measurements. In one embodiment, thecontroller operates the fan during smoke measurements. In oneembodiment, the controller operates the fan between smoke measurements(e.g., between pulses of radiation from the emitter 902) and does notoperate the fan during smoke measurements. In one embodiment, when asmoke measurement indicates that there may be smoke present, thecontroller 202 operates the fan 930 for a relatively brief period (totry and draw additional smoke into the chamber 901) and then takesadditional smoke measurements. The fan increases air exchange with thesmoke chamber 901 and thus, makes the smoke sensor 900 respondrelatively more quickly to changes in the level of smoke near the sensor900. Thus, for example, in some configurations, smoke may becometemporarily trapped in the smoke chamber 901 and cause the sensor 900 toreport the presence of smoke even after smoke in the room hasdissipated. By using the fan, the controller 202 can cause relativelymore air exchange of the smoke chamber, clear trapped smoke from thechamber 901, and thereby cause the sensor 900 to respond relatively morerapidly to changes in the ambient smoke level.

In one embodiment, the controller 202 operates the fan in response toone or more commands from the computer 113. Thus, for example, if thecomputer 113 receives smoke measurements from the sensor unit 103, whichis located relatively near the sensor unit 102 (e.g., in the sameapartment, same hallway, same portion of a building, etc.) then thecomputer 113 can instruct the controller 202 in the sensor unit 102 toactivate the fan 930 in order to improve the response time of the sensorunit 102. In one embodiment, the computer 113 instructs the sensor unit102 to first take one or more smoke sensor measurements (withoutactivating the fan 930) and report these first measurements back to thecomputer 113. The computer 113 can then instruct the controller 202 toactive the fan 930 and then take one or more smoke sensor measurements(with the fan 930 running/and or after the fan 930 has been stopped) andreport the second smoke sensor measurements. If either the first orsecond set of smoke sensor measurements indicates smoke is present, thenthe computer 113 can report that the area affected by smoke includes thearea proximate to both the sensor units 102 and 103.

In one embodiment, the controller 202 stores three threshold levels. Thefirst threshold level corresponds to one or more first measurementstaken by the photo-sensor 903 when the emitter 902 is not operating.Thus, the first threshold corresponds generally to the dark current ofthe photo-sensor 903 and ambient light detected by the photo-sensor 903.In one embodiment, the first threshold is computed by selecting themaximum of the first measurements. In one embodiment, the firstthreshold is computed by averaging one or more of the firstmeasurements. The resulting first threshold is then stored. In oneembodiment, the ambient temperature present at the time of the firstmeasurements is recorded. A correction factor can be applied to thefirst threshold to account for ambient temperature. In one embodiment,the temperature correction is provided by analog circuitry associatedwith the photo-sensor 903 (e.g., by thermistors 916 used to compensatethe gain characteristics of the amplifier 906). In one embodiment, thetemperature correction is computed digitally by the controller 202 usingdata from the temperature sensor 920. In one embodiment, both analogcompensation using the temperature sensors 916, and digital compensationusing data from the temperature sensor 920 are used. The resulting firstthreshold is then stored.

The first threshold can vary according to the temperature of thephoto-sensor 903 and the presence or absence of ambient light. Thus,when taking actual smoke measurements or running diagnostics, thecontroller 202 can re-measure the output of the photo-sensor 903 whenthe emitter 902 is not operating, re-compute the first threshold, andcompare the re-computed first threshold value with the stored firstthreshold value. If the re-computed first threshold value differs fromthe stored first threshold value by a specified error threshold, thenthe controller 202 can report to the monitoring computer 113 that ananomalous condition or fault condition has occurred.

The second threshold corresponds to one or more second measurementstaken by the photo-sensor 903 when the emitter 902 is pulsed, but whensmoke is not expected to be present. Thus in a scattering-type smokesensor, the second threshold corresponds generally to the light detectedby the photo-sensor 903 that is scattered by the chamber 901. In anobscuration-type smoke sensor, the second threshold correspondsgenerally to the light detected by the photo-sensor 903 from the emitter902. In one embodiment, the second threshold is computed by selectingthe maximum of the second measurements. In one embodiment, the secondthreshold is computed by averaging one or more of the secondmeasurements. In one embodiment, the ambient temperature present at thetime of the second measurements is recorded. A correction factor can beapplied to the second threshold to account for ambient temperature. Inone embodiment, the temperature correction is provided by analogcircuitry associated with the photo-sensor 903 (e.g., by thermistors 916used to compensate the gain characteristics of the amplifier 906). Inone embodiment, the temperature correction is computed digitally by thecontroller 202 using data from the temperature sensor 920. In oneembodiment, both analog compensation using the temperature sensors 916,and digital compensation using data from the temperature sensor 920 areused.

The resulting second threshold is then stored. Thus, when runningdiagnostics, the controller 202 can re-measure the output of thephoto-sensor 903 when the emitter 902 is operating, re-compute thesecond threshold, and compare the re-computed second threshold valuewith the stored second threshold value. If the re-computed secondthreshold value differs from the stored second threshold value by aspecified error threshold, then the controller 202 can report to themonitoring computer 113 that an anomalous condition or fault conditionhas occurred. Typically, the second threshold will be relatively largerthan the first threshold. Thus, in one embodiment, the controller 202can compare the first threshold with the second threshold. If the secondthreshold is not relatively larger than the first threshold, then ananomalous condition or error condition can be reported.

The third threshold corresponds to the reporting threshold describedabove, and is the threshold level at which the controller determinesthat smoke may be present and that the sensor measurements should bereported to the monitoring computer 113. In one embodiment, thecontroller 202 computes the third threshold as a function of the secondthreshold (e.g., as a percentage increase, as a fixed increase, etc.).In one embodiment, the controller 202 computes the third threshold as afunction of the first threshold and the second threshold. In oneembodiment, the controller 202 reports the second threshold (and,optionally the first threshold) to the monitoring computer 113, and themonitoring computer computes the desired third threshold and sends thethird threshold to the controller 202. As described in connection withFIG. 6, if the measured data from the photo sensor 903 exceeds the thirdthreshold (the reporting threshold) then the controller 202 sends themeasured smoke data to the monitoring computer 113. Moreover, asdescribed above, the value of the third threshold (the reportingthreshold) is adjustable and can be lowered relatively closer to thesecond threshold to increase the sensitivity of the sensor unit 102.

The sensitivity of the sensor unit 102 increases as the third threshold(the reporting threshold) approaches the second threshold, and thesensitivity of the sensor unit 102 decreases as the third thresholdincreased above the second threshold. Moreover, the sensitivity of thesensor unit 102 increases as the second threshold decreases. Althoughthe second threshold should typically not be lower than the firstthreshold, the value of the first threshold can vary due to thetemperature of the photo-sensor 903 and the ambient light. Thus, in oneembodiment, the controller periodically re-measures the first and secondthresholds and re-computes the third threshold to provide relativelyhigh sensitivity as allowed by current conditions.

In one embodiment, the controller computes both the second and thirdthreshold values based on the measured first threshold value. Since thefirst threshold value is measured when the emitter is 902 is notoperating, the first threshold value is relatively independent of thepresence of smoke and depends primarily on the ambient temperature andthe presence of ambient light. Thus, the controller can re-measure thefirst threshold and compute the second threshold using the stored firstand second threshold values obtained during calibration.

In one embodiment, the smoke sensor 900 is configured as a replaceablemodule. A connector 940 is provided to the smoke sensor 900 to allow thesmoke sensor 900 to be provided to the controller 202. In oneembodiment, the smoke sensor 900 is calibrated (e.g., calibrated at thefactory, calibrated before installation, calibrated during installation,etc.) and the calibration data is provided to a calibration module 941.The calibration module 941 provides the calibration data to thecontroller 202 so that the controller 202 knows the characteristics ofthe smoke sensor 900. In one embodiment, the calibration module 941 isconfigured as a read-only memory (ROM) that provides calibration data.

In one embodiment, the calibration module 941 is configured as a ROMthat provides software used by the controller 202 to, at least in part,operate the sensor 900. By providing software with the sensor module900, different types of sensor modules, upgraded sensor modules, etc.,can be plugged into the sensor unit 102 for use by the controller 202.In one embodiment, flash memory is provided (in the calibration module941 and/or in the controller 202) to allow the monitoring computer 113or installation personal to download new software into the sensor unit102.

In one embodiment, calibration data provided by the calibration module941 includes expected ranges for the first threshold and/or the secondthreshold. The controller 202 can report a fault if the actual firstand/or second threshold values measured (or computed) by the controller202 fall outside the ranges specified by the calibration module 941.

FIG. 12 shows one embodiment of temperature compensation for the emitter902 and the photo-detector 903. In the embodiment of FIG. 12, an inputto the emitter 902 is provided through a resistor 1201 to a controlinput of a transistor 1202 (the transistor 1202 is shown as an NPNtransistor, but one of skill in the art will recognize the transistor1202 can also be configured as a PNP transistor, FET transistor, MOSFETtransistor, etc.). The transistor 1202 is configured such that when thetransistor 1202 is in a conducting state, the transistor 1202 providescurrent from a photo-emitter diode 1203 to ground. Current from aV+supply is provided to the diode 1203 by a parallel combination of aresistor 1204 and a thermistor 1205. In one embodiment, the thermistor1205 has a negative temperature coefficient. In one embodiment, theresistance of the resistor 1204 is relatively smaller than theresistance of the thermistor 1205. In one embodiment, the resistance ofthe resistor 1204 is substantially smaller than the resistance of thethermistor 1205.

In the embodiment of FIG. 12, in photo-detector 903, the V+supply isprovided through a resistor 1211 to a reverse-biased photo-detectordiode 1212. The photo-diode 1212 is provided to ground through aresistor 1213. The ungrounded terminal of the resistor 1213 is alsoprovided to an input of an amplifier 1214. An output of the amplifier1214 is provided to ground through a thermistor 1215 to an input of anamplifier 1217. The input of the amplifier 1217 is also provided toground through a resistor 1216, such that the thermistor 1215 and theresistor 1216 form a voltage divider. In one embodiment, the thermistor1215 has a negative temperature coefficient. An output of the amplifier1217 is provided as an output of the photo-detector 903.

The thermistor 1205 provides temperature compensation for thephoto-emitter diode 1203 to stabilize the operation of the diode 1203with respect to temperature. The thermistor 1215 provides temperaturecompensation for the photo-detector diode 1203 to stabilize theoperation of the diode 1212 with respect to temperature. Thus, theembodiments of the emitter 902 and photo-detector 903 shown in FIG. 12provide an output that is relatively more stable with temperaturechanges than embodiments that are not temperature corrected. The use oftemperature correction shown in FIG. 12 allows the sensor unit 102 tooperate at relatively higher sensitivity without producing excess falsealarms.

Use of one or more, or combined use of two or more, of the techniquesdisclosed above, (e.g., variable threshold, temperature compensation,multi-threshold calibration, tend analysis, fans, etc.) allows thesensor unit 102 to operate relatively reliably at relatively highersensitivities than prior art sensor units. The ability to operaterelatively reliably at higher sensitivities (e.g., to detect smoke atlower concentrations without generating an unacceptable number of falsealarms) allows the system 100 to detect fires or other dangerousconditions more quickly and with greater accuracy than prior artsystems.

It will be evident to those skilled in the art that the invention is notlimited to the details of the foregoing illustrated embodiments and thatthe present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributed thereof; furthermore,various omissions, substitutions and changes may be made withoutdeparting from the spirit of the invention. For example, althoughspecific embodiments are described in terms of the 900 MHz frequencyband, one of ordinary skill in the art will recognize that frequencybands above and below 900 MHz can be used as well. The wireless systemcan be configured to operate on one or more frequency bands, such as,for example, the HF band, the VHF band, the UHF band, the Microwaveband, the Millimeter wave band, etc. One of ordinary skill in the artwill further recognize that techniques other than spread spectrum canalso be used. The modulation is not limited to any particular modulationmethod, such that modulation scheme used can be, for example, frequencymodulation, phase modulation, amplitude modulation, combinationsthereof, etc. The foregoing description of the embodiments is,therefore, to be considered in all respects as illustrative and notrestrictive, with the scope of the invention being delineated by theappended claims and their equivalents.

What is claimed is:
 1. A wireless device, comprising: a smoke sensorconfigured to obtain measurement data regarding a level of smoke; awireless transceiver capable of wirelessly transmitting and receivinginformation to and from an electronic device located remotely from thewireless device; a power source for powering operation of the wirelessdevice; and a controller operatively coupled to the smoke sensor,wireless transceiver, and the power source, and configured to: operatethe wireless device in a sleep mode while the smoke sensor obtains themeasurement data, wherein power consumption of the wireless device fromthe power source is lower when the wireless device operates in the sleepmode as compared to when the wireless device operates in an awake mode;determine, from the measurement data, whether the level of smoke hasexceeded a reporting threshold; and in response to determining that thelevel of smoke has exceeded the reporting threshold: determine a noticelevel, warning level, and/or alarm level based on: the level of smoke,and/or a rate of rise of the level of smoke; determine whether thenotice level, warning level, and/or alarm level has been exceeded; andcommunicate a signal indicative of the notice level, warning level,and/or alarm level being exceeded when it is determined that the noticelevel, warning level, and/or alarm level has been exceeded.
 2. Thewireless device of claim 1, wherein the wireless transceiver isconfigured to communicate the signal while the wireless device isoperating in the awake mode.
 3. The wireless device of claim 2, whereinthe controller is configured to: determine whether the level of smokehas exceeded the reporting threshold while operating the wireless devicein the sleep mode; and temporarily switch the wireless device from thesleep mode to the awake mode in response to determining that the noticelevel, warning level, and/or alarm level has been exceeded; andcommunicate the signal indicative of the notice level, warning level,and/or alarm level being exceeded while operating the wireless device inthe awake mode.
 4. The wireless device of claim 1, wherein thecontroller is configured to temporarily switch the wireless device fromthe sleep mode to the awake mode periodically.
 5. The wireless device ofclaim 4, wherein the controller is configured to communicate themeasurement data obtained by the smoke sensor while the wireless deviceis operating in the awake mode.
 6. The wireless device of claim 1,wherein the controller is configured to: determine, prior tocommunicating the signal, an available wireless frequency channel; andcommunicate the signal on the available wireless frequency channel. 7.The wireless device of claim 1, wherein the controller is configured tocommunicate the signal a plurality of times until the wireless devicereceives an acknowledgement that the signal has been received.
 8. Thewireless device of claim 7, wherein the controller is configured tocommunicate the signal a plurality of times, based on a priority of thenotice level, warning level, and/or alarm level.
 9. A method ofoperating a wireless device, comprising: powering the wireless devicewith a power source; operating the wireless device in a sleep mode,wherein power consumption of the wireless device from the power sourceis lower when the wireless device operates in the sleep mode as comparedto when the wireless device operates in an awake mode; obtaining, whileoperating the wireless device in the sleep mode and from a smoke sensorof the wireless device, measurement data regarding a level of smoke;determining, from the measurement data, whether the level of smoke hasexceeded a reporting threshold; and in response to determining that thelevel of smoke has exceeded the reporting threshold: determining anotice level, warning level, and/or alarm level based on: the level ofsmoke, and/or a rate of rise of the level of smoke; determining whetherthe notice level, warning level, and/or alarm level has been exceeded;and communicating, to an electronic device located remotely from thewireless device and via a wireless transceiver of the wireless device, asignal indicative of the notice level, warning level, and/or alarm levelbeing exceeded when it is determined that the notice level, warninglevel, and/or alarm level has been exceeded.
 10. The method of operatinga wireless device of claim 9, further comprising communicating thesignal using spread-spectrum techniques.
 11. The method of operating awireless device of claim 10, further comprising receiving a uniqueidentifier for the wireless device from another wireless device during aconfiguration period, the unique identifier distinguishing the wirelessdevice from other wireless device in a network.
 12. The method ofoperating a wireless device of claim 11, further including embedding, inthe signal and prior to communicating the signal, the unique identifierof the wireless device.
 13. The method of operating a wireless device ofclaim 9, wherein communicating the signal occurs while the wirelessdevice is in the awake mode, and the method further comprises: aftercommunicating the signal, listening for instructions while in the awakemode and before returning back to the sleep mode.
 14. The method ofoperating a wireless device of claim 9, further comprising: in responseto determining that the notice level, warning level, and/or alarm levelhas been exceeded: controlling operation of a fuel and/or power source.15. The method of operating a wireless device of claim 14, whereincontrolling operation of a fuel and/or power source includes controllinga gas shutoff valve to shut off gas supply to a water heater and/orfurnace.
 16. The method of operating a wireless device of claim 9,further comprising: listening for one or more instructions that areaddressed to a unique identifier associated with the wireless devicewhile operating in the awake mode, and, in response to receiving the oneor more instructions, perform one or more functions requested by the oneor more instructions, the one or more instructions being selected fromthe group consisting of: an instruction for the wireless device to wakeup, an instruction for the wireless device to report its battery status,and an instruction for the wireless device to change its wake-upinterval; and ignoring any instructions that are not addressed to theunique identifier associated with the wireless device.
 17. A wirelessdevice for smoke detection, comprising: means for powering the wirelessdevice; means for operating the wireless device in a sleep mode, whereinpower consumption of the wireless device from the means for powering thewireless device is lower when the wireless device operates in the sleepmode as compared to when the wireless device operates in an awake mode;means for obtaining, while operating the wireless device in the sleepmode, measurement data regarding a level of smoke; means fordetermining, from the measurement data, whether the level of smoke hasexceeded a reporting threshold; means for determining a notice level,warning level, and/or alarm level based on: the level of smoke, and/or arate of rise of the level of smoke; means for determining whether thenotice level, warning level, and/or alarm level has been exceeded; andmeans for wirelessly communicating, to an electronic device locatedremotely from the wireless device, a signal indicative of the noticelevel, warning level, and/or alarm level being exceeded when it isdetermined that the notice level, warning level, and/or alarm level hasbeen exceeded.
 18. The wireless device for smoke detection of claim 17,wherein: the means for determining a notice level, warning level, and/oralarm level includes means for determining an alarm level for a level ofsmoke that is relatively high and a rate of rise of the level of smokeis relatively high; the means for determining whether the notice level,warning level, and/or alarm level has been exceeded includes means fordetermining whether a measured level of smoke exceeds the relativelyhigh level of smoke associated with the alarm level and whether a rateof rise of the measured level of smoke exceeds the relatively high rateof rise of the level of smoke associated with the alarm level; and themeans for wirelessly communicating the signal includes means forwirelessly communicating the signal indicative of the alarm level beingexceeded when it is determined that the measured level of smoke exceedsthe relatively high level of smoke associated with the alarm level andwhen it is determined that a rate of rise of the measured level of smokeexceeds the relatively high rate of rise of the level of smokeassociated with the alarm level.
 19. The wireless device for smokedetection of claim 18, wherein: the means for determining a noticelevel, warning level, and/or alarm level includes means for determininga notice level for a level of smoke that is relatively low as comparedto the alarm level and a rate of rise of the level of smoke isrelatively low as compared to the alarm level; the means for determiningwhether the notice level, warning level, and/or alarm level has beenexceeded includes means for determining whether the measured level ofsmoke exceeds the relatively low level of smoke associated with thenotice level and whether a rate of rise of the measured level of smokeexceeds the relatively low rate of rise of the level of smoke associatedwith the notice level; and the means for wirelessly communicating thesignal includes means for wirelessly communicating the signal indicativeof the notice level being exceeded when it is determined that themeasured level of smoke exceeds the relatively low level of smokeassociated with the notice level and when it is determined that a rateof rise of the measured level of smoke exceeds the relatively low rateof rise of the level of smoke associated with the notice level.
 20. Thewireless device for smoke detection of claim 17, further comprising:means for determining a fault condition of the wireless device afterinitialization if the wireless device, the fault condition beingselected from the group consisting of: activation of a tamper sensor,low battery, and internal fault; and means for wirelessly communicatinginformation indicative of the fault condition from the wireless deviceto the electronic device located remote from the wireless device.